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FPGA interconnection networks with capacitive boosting in strong and weak inversionEslami, Fatemeh 22 August 2012 (has links)
Designers of Field-Programmable Gate Arrays (FPGAs) are always striving to
improve the speed of their designs. The propagation delay of FPGA interconnection networks is a major challenge and continues to grow with newer technologies.
FPGAs interconnection networks are implemented using NMOS pass transistor based
multiplexers followed by buffers. The threshold voltage drop across an NMOS device
degrades the high logic value, and results in unbalanced rising and falling edges, static
power consumption due to the crowbar currents, and reduced noise margins. In this
work, circuit design techniques to construct interconnection circuit with capacitive
boosting are proposed. By using capacitive boosting in FPGAs interconnection networks, the signal transitions are accelerated and the crowbar currents of downstream
buffers are reduced. In addition, buffers can be non-skewed or slightly skewed to improve noise immunity of the interconnection network. Results indicate that by using
the presented circuit design technique, the propagation delay can be reduced by at
least 10% versus prior art at the expense of a slight increase in silicon area.
In addition, in a bid to reduce power consumption in reconfigurable arrays, operation in weak inversion region has been suggested. Current programmable interconnections cannot be directly used in this region due to a very poor propagation delay
and sensitivity to Process-Voltage-Temperature (PVT) variations. This work also focuses on designing a common structure for FPGAs interconnection networks that
can operate in both strong and weak inversion. We propose to use capacitive boosting together with a new circuit design technique, called Twins transmission gates in
implementing FPGA interconnect multiplexers. We also propose to use capacitive
boosting in designing buffers. This way, the operation region of the interconnection
circuitry is shifted away from weak inversion toward strong inversion resulting in improved speed and enhanced tolerance to PVT variations. Simulation results indicate
using capacitive boosting to implement the interconnection network can have a significant influence on delay and tolerance to variations. The interconnection network
with capacitive boosting is at least 34% faster than prior art in weak inversion. / Graduate
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On designing coarse grain reconfigurable arrays to operate in weak inversionRoss, Dian Marie 17 December 2012 (has links)
Field Programmable Gate Arrays (FPGAs) support the reconfigurable computing paradigm by providing an integrated circuit hardware platform that facilitates
software like reconfigurability. The addition of an embedded microprocessor and peripherals to traditional FPGA Combinational Logic Blocks (CLBs) interleaved with
interconnections has effectively resulted in a programmable system on-chip. FPGAs
are used to support flexible implementations of Application Specific Integrated Circuit (ASIC) functions. Because FPGAs are reconfigurable, they often are used in
place of ASICs during the cicuit design process. FPGAs are also used when only a
small number of ICs are required: ASICs necessitate large manufacturing runs to be
economically viable; for smaller runs the use of FPGAs is an economic alternative.
Application domains of interest, such as intelligent guidance systems, medical
devices, and sensors, often require low power, inexpensive calculation of trance-
dental functions. COordinate Rotation DIgital Computer (CORDIC) is an iterative algorithm used to emmulate hardware expensive multipliers, such as Multiply/ACculmulate (MAC) units, with only shift and add operations. However, because CORDIC is a sequential algorithm, characterized as having the latency of a
serial multiplier, techniques that speed up computational performance have many
applications.To this end, three implementations of standard CORDIC, (i) unrolled hardwired,
(ii) unrolled programmable, and (iii) rolled programmable, were implemented on four
Xilinx FPGA families: Virtex-4, -5, and -6, and Spartan-6. Although hardwired
unrolled was found to have the greatest speed at the expense of no runtime flexibility,
and rolled programmable was found to have the greatest flexibility and lowest silicon
area consumption at the expense of the longest propagation delay, improvements to
CORDIC implementations were still sought.
Three parallelized CORDIC techniques, P-CORDIC, Flat-CORDIC, and
Para-CORDIC, were implemented on the same four FPGA families. P-CORDIC
and Flat-CORDIC, were shown to have the lowest latency under various conditions;
Para-CORDIC was found to perform well in deeply pipelined, high throughput circuits. Design rules for when to use standard versus precomputation CORDIC techniques are presented.
To address the low power requirements of many applications of interest, the Unfolded Multiplexor-LRB (UMUX-LRB), patent held by Sima, et al, was analyzed in
weak inversion across four transistor technology nodes (180nm, 130nm, 90nm, and
65nm). Previous was also expanded from strong inversion across 180nm, 130nm, and
90nm technology nodes to also include 65nm.
The UMUX-LRB interconnection network is based upon the Xilinx commercial
interconnection network. Therefore, this network (MUX-LRB), and another static
circuit technique, CMOS-Transmission Gates (CMOS-TG), were profiled across all
four technology nodes to provide a baseline of comparision. This analysis found
the UMUX-LRB to have the smallest and most balanced rising and falling edge
propagation delay, in addition to having the greatest reliability for temperature and
process variation. / Graduate
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